It has been long recognized that the foot is the most difficult area to maintain sufficiently warm for comfort. Because the foot is an extremity, blood flow to this area is less effective in maintaining warmth. Maintaining the warmth of the foot area is especially difficult when special purpose footwear, such as ski boots are utilized. Ski boots have been developed to a high level of performance in transferring the wearer's motions to the skis and in minimizing the possibility of injury. Performance and safety considerations however are not necessarily compatible with good insulative qualities. Similar considerations apply to other footwear such as hiking boots. The problems of maintaining warmth on the foot are most difficult during periods of inactivity.
In recognition of the impracticality in maintaining foot warmth solely through insulative means, the prior art has developed a variety of electrically powered foot warmers. In a typical device, the electrical foot warmer consists of an electrical resistance heating element built into the shoe or boot or incorporated into a special purpose sock. Electrical energy is provided by a battery clipped to the boot or to the user's belt for example. Such devices have not seen wide spread application due to several independent deficiencies. Frequently such devices result in an impractical short battery life resulting from the lack of a practical switch, excessive current drain, or exposure of the battery to the elements. Other such devices have been uncomfortable to wear because the electrical heating elements is of a size and shape that irritates the ball of the user's foot. Still another problem with such devices is that the heat generated by the electrical resistance element is not positioned for maximum benefit and alternatively the positioning and configuration of the heating element results in uncomfortable hot spots.
Therefore, it is desirable to have a battery powered foot warmer that extends battery life and provides controlled and selective application of heat. Such a device is particularly valuable where the device may be installed in a variety of footwear and used without any uncomfortable pressure points on the wearer's foot.